Detailed inspection throughout the lifetime of a safety-critical part is absolutely essential.  The tail mounted engine on the DC-10 aircraft for United Airlines Flight 232 had left the manufacturing foundry with undetected microscopic defects.  However, when establishing the safe operational lifetime, it was assumed that all parts were defect free.  After 15 years of operations, numerous inspection teams failed to detect the growth of cracks from these defects, and the initial defect-free assumptions were never re-evaluated.  On July 19, 1989, that engine exploded well before its set operational lifetime, severing all three hydraulic fluid lines.  The pilots of Flight 232 had never trained for a complete loss of hydraulic controls nor were there any operating procedures for handling such a scenario.  Still, because they thoroughly understood the DC-10 system, they were able to regain just enough control to crash land the plane using only the remaining engine throttles.   While it is impossible to predict and then train for every conceivable situation, even some known scenarios are so complex and dependent on other variables that official documented procedures can be ineffective.  Therefore, it is critical that NASA operators have a thorough understanding of our systems and operations, so that they are able to successfully navigate situations for which they were not explicitly trained.